1. Field of the Invention
The present invention relates to quick release nuts, and relates particularly, but not exclusively, to quick release nuts for use in hydraulic tensioning of bolts.
2. Description of the Prior Art
Tensioned bolts are used in many applications, such as connections between flanges at the ends of adjacent lengths of pipeline. The bolt is tensioned by means of a hydraulic bolt tensioning tool, and a nut is screwed onto the bolt while under tension. The bolt tensioning tool has a hydraulic piston which act on a reaction member in the form of a reaction nut screwed onto the free end of the bolt and which grips the bolt. The bolt is extended when axial pressure is applied to the nut by means of the tensioning tool, and when the hydraulic pressure operating within the tensioning tool is released, the bolt contracts to effect a secure connection.
The length of that part of the bolt protruding beyond the hydraulic bolt tensioning tool can be significant, which can cause difficulties if the reaction nut must be screwed onto the bolt, or removed from it after the connection using a tensioned bolt has been made. This is especially so in the case of damaged or rusted threads, or hostile environments such as undersea applications, where this process becomes time consuming and therefore expensive.
An attempted solution to this problem is disclosed in U.S. Pat. No. 4,438,901 and GB2143608, in which bolt tensioners incorporating a collet with radially displaceable segments are provided. However, bolt tensioners of this type suffer from the drawback that they are mechanically complex and difficult to use because of their bulk and weight.
GB2193549 and EP0408239 disclose prior art nuts for use with bolt tensioning tools and in which a split reaction nut is provided. The split nut has a surface engaged by a corresponding surface on the piston of the hydraulic cylinder/piston assembly of the bolt tensioning tool and is provided in two halves which can be moved apart to enable easier mounting to and removal from the bolt.
In particular, the split nut of EP0408239 is provided with a pair of guide pins along which the two halves of the split nut are slidable relative to each other between an inoperative position in which segments are spaced radially apart and an operative position in which the segments form a nut which can engage the thread of the bolt. The segments are biassed towards their inoperative position by means of coil springs mounted on the guide pins which react between end faces of the segments, and are held in their operative position by means of ball bearings provided in the segments which are urged by means of a coil spring into engagement with a circumferential groove in the guide pins.
This prior art split nut suffers from the disadvantage that the force retaining the segments in their operative position is dependent upon the resilience and adjustment of the coil spring, as a result of which it is often difficult to effect positive and repeatable engagement of the ball bearings in the groove. Also, a significant force needs to be applied to disengage the segments from each other towards the inoperative position, as a result of which disengagement of the halves of the nut from their operative position becomes difficult.
Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art.
According to the present invention, there is provided a quick release nut comprising:
a plurality of body members adapted to be placed around a shaft of a bolt and having a surface adapted to engage the shaft of the bolt, wherein said body members are movable between an operative position, in which said surface engages the shaft of the bolt in use, and an inoperative position in which said body members are spaced further apart from each other than in said operative position; and
fastening means for fastening said body members in said operative position and comprising, for each pair of adjacent body members in a circumferential direction around said surface, at least one elongate sliding member provided on a body member of said pair and slidable in a respective first recess provided in the other body member of said pair, and at least one retaining member provided on at least one said sliding member of the or each said pair, wherein the or each said retaining member is adapted to engage a respective second recess in the corresponding first recess to releasably retain the body members in the operative position.
By providing retaining members provided on at least one sliding member of the or each pair of body members which are adapted to engage in corresponding second recesses in the first recesses, this provides the advantage of making the retaining means more accessible than in the case of the prior art. This provides the further advantage that the retaining force of the retaining members can be more easily adjusted, and releasing of the retaining members from the second recesses is simplified.
The surface may be substantially part-cylindrical.
The surface is preferably threaded.
The nut preferably further comprises a portion of tapering lateral width.
By providing a portion of tapering lateral width, this provides the advantage that the application of pressure by means of a correspondingly shaped surface on the bolt tensioning tool causes the body members to be urged towards each other, thus more tightly gripping the shaft of the bolt.
The nut may further comprise a respective first biassing means for urging the or each said retaining member into engagement with the corresponding second recess.
In a preferred embodiment, at least one said retaining member is a ball bearing received in a respective third recess in the corresponding sliding member.
In a preferred embodiment, at least one said sliding member comprises a pin slidably mounted in a respective housing, wherein the or each retaining member of said sliding member is released in use from the corresponding second recess by sliding said pin relative to said housing.
The nut may further comprise a respective second biassing means for urging at least one said pair of body members apart.